If you are setting a server or your own machine with SSH key password-less, then you will likely get this error Authentication refused bad ownership or modes.
This happens for your own security, SSH is very picky when dealing with ~/.ssh and this is the right thing, people apart from yourself should not be able to move, read or edit your ~/.ssh.
To fix this issue all you have to do is set the right permission.
chmod go-w ~/
chmod 700 ~/.ssh
chmod 600 ~/.ssh/authorized_keys
Now you should be able to authenticate just fine.